Effects of applying high-pass filtering in pelvimetry with Martius images

Aim: The aim of this study is to investigate whether the results of pelvimetry using original radiographic Martius images and the same images with high-pass filtering applied ("edge images") would be consistent.

Methods: A total of 30 primagravidas were included in this study. Three obstetricians independently measured the anteroposterior and transverse diameters of the pelvic inlet in the original and the edge images, recording the x- and y-coordinates of the four endpoints. A Wilcoxon signed rank sum test was performed on the coordinate data to evaluate differences between the original and edge images.

Results: In the analysis of all coordinate data, statistically significant differences were found in both x- and y-coordinates of the sacral promontory point (SPP). In the y-coordinate of the SPP, a statistically significant difference was found in 9 of 30 pairs of images, and in all 9 the anteroposterior diameter was shorter in the edge images compared to the original images due to the more caudal placement of the SPP.

Conclusions: The coordinates of the SPP on original radiographs and their edge images were not consistent in pelvimetry using Martius images. Our results suggest that improved image contrast will allow obstetricians to better assess pelvic narrowing and cephalopelvic disproportion and even reduce radiographic dose, thereby reducing risks for pregnant women and their fetuses.